alot with the ram is how you tweak windows, if youre running on default and leave all your apps going during games you will need alot of ram.
When they bench it's a clean install with only the bare drivers and no other apps running, they don't acount for a dirty system. If you set win to performance and keep your system clean,defraged and turn off all apps but the game one gig is all you really need. If you just install a game and hit the icon to play, you have half your ram filled with junk[ virus scans, pop up blocker and the like]. Every thing wants to run in ram now even if you don't need it 90% of time, sloppy coding really. I would also defrag before and after you install a large program. So many people blame the vid card when it's really the harddrive being read because the ram is full.
I'm sure vista will be a sloppy ass ram hog so two gigs is a good idea. I was hoping MS would take a hint from linux and make a smarter OS but it doesnt look like it. With all the flavors of vista one should be gaming, but isn't